<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /* 水平偏移，上下偏移，阴影半径，阴影颜色 */
        #div-shadow{
            width: 100px;
            height: 100px;
            border: 10px solid red;
            margin-bottom: 100px;
            box-shadow: 10px 3px 4px rgb(155, 240, 155);
        }
        /* margin：0 auto 居中
          要求：块元素：块元素有固定宽度
          
         */
        img{
            margin: 0px 220px;
            border-radius: 30px;
            box-shadow: 10px 10px 100px yellow;
        }
    </style>
</head>
<body>
    <div id="div-shadow"></div>
    <img src="image/QQ截图20210425162248.png" alt="">

    <div style="display: block;text-align: center;margin: 30px auto;">a</div>

    <img src="image/QQ截图20210425162248.png" alt="" style="float: center;">
</body>
</html>